1. Field of the Invention
The present invention relates to an apparatus for working on the surfaces of ship hulls, aircraft fuselages, barges, storage tanks, and the like. In particular, the present invention relates to a contour-following apparatus for supporting and guiding tools such as ultra-high pressure water sprayers, sand and grit blasters, paint sprayers, and lasers.
2. Discussion of Background
The shipping industry is a vital and growing part of the global economy. At least 25,000 oceangoing vessels of weight 1,000 gross tons or more are presently in operation (this estimate does not include vessels that operate exclusively on inland waterways, military vessels, and special-purpose vessels such as icebreakers and cable ships. (The terms "ship" and "vessel" are used herein to refer to all watercraft, including boats, barges, tankers, cargo ships, freighters, cruisers, container ships, submarines, tankers, supertankers, aircraft carriers, and so forth.)
The external surfaces of ship hulls are generally treated with coatings containing anti-fouling agents and rust preventatives to inhibit marine growth and minimize corrosion. However, even the most durable coatings eventually deteriorate and must be replaced to prevent corrosion of the hull.
Protective coatings also help preserve the smoothness of a submerged surface. In general, the smoother the surface of any submerged portion of a ship (such as the hull or the propeller blades), the greater the fuel efficiency and the speed of the vessel. Roughness caused by barnacles and other marine growth, degradation of hull coatings, and deterioration of propeller surfaces can adversely affect the performance of the ship. Fouling also affects the hull coating material, eventually leading to corrosion and metal fatigue. Corrosion damage can result in expensive repairs, downtime, and, in severe cases, to premature scrapping of the ship.
In order to forestall these deleterious effects, the outer surfaces of ship hulls are cleaned periodically in dry dock to remove old coating material (including paint), corrosion, and marine growth, and new coatings are applied. (As used herein, the terms "cleaning" and "stripping" refer to removal of old paint and other coatings, corrosion, etc. from the surface of a ship hull or other surface.) In general, the cleaner and smoother the hull surface after cleaning, the longer-lasting and more effective the new coating. Thus, effective removal of old coatings, corrosion, and marine growth not only extends the lifetime of the new coating but reduces future maintenance expenses and resulting downtime. These maintenance questions are also a concern for aircraft and storage tanks, which also have exposed surfaces that are treated with corrosion-resistant or weather-resistant coatings.
A number of different techniques are used to clean ship hulls. Perhaps the most prevalent technique involves the use of sand blasting or grit blasting to remove paint, corrosion, and marine growth from the hull and expose the bare steel for the application of new coatings. Although sand blasting is widely used, it has several disadvantages including abrasion to the skin of the personnel performing the blasting, an increase in the amount of materials which must be recovered and disposed of, and undesired metallurgical changes to the steel surface being impacted by the silica particles.
Another technique that is rapidly gaining popularity is the use of ultra-high pressure water. Large compressors are used to generate pressures up to 60,000 psi to force the water through small orifices located close to the metal surface to be cleaned. The kinetic energy of the water at those elevated pressures is adequate to remove substantially all marine growth, paint and primer down to bare metal. Unlike sand blasting or grit blasting, this technique does not generate abrasive projectiles, there is no increase in the amount of materials to dispose of, and there are no metallurgical changes to the steel surfaces being cleaned.
Cleaning can be accomplished by manual or automated techniques. Manual cleaning is both dangerous and time consuming: the operators must work by hand with ultra-high pressure water jet wands that can produce thrusts as high as 50 pounds. The kinetic energy of the ultra-high pressure water can easily cut and lacerate human flesh, making the hand-held wands very dangerous to use. To access all the surfaces of a ship that may need to be cleaned, the operator of a water jet must either crouch underneath the hull or be supported by scaffolding or a boom-operated basket to access the sides of the ship. The efficiency of surface cleaning varies from person to person based on the techniques and equipment used: a four-person crew can average about 60 square feet per hour with manual equipment; a two-person crew can clean as much as 250 square feet per hour with automated equipment. Therefore, many dry dock operators prefer remote-controlled apparatus that allows the user to direct the position and movement of the cleaning head.
While most of the surface of a ship hull is approximately flat, the overall shape of the hull is composed of three-dimensional contours. These contours are predominant in the bow, stern and bottom. Any useful remote-controlled cleaning apparatus must accommodate this curvature, for example, by allowing the user to tilt an instrument carriage to maintain approximately uniform spacing between the carriage and the particular area of the hull being worked on.
Presently-available apparatus for cleaning hulls includes a mobile carrier disclosed by Goldbach, et al. (U.S. Pat. No. 5,540,172). The carrier, which has four sloping, adjustable-length legs, supports an abrasive blaster which is movable along a pair of rails having limit switches at both ends. The rail end connections are somewhat articulatable, thereby allowing the user to adjust the positions of the rails to the orientation and curvature of the hull by adjusting the lengths of the legs. A control panel allows the operator to control movement of the blaster and the carrier, spraying of abrasive, and for extending and retracting the legs to conform the positions of the rail ends to the bottom of the ship hull.
Janusz (U.S. Pat. No. 5,138,800) discloses a positioning apparatus for working on an airplane fuselage. The apparatus is attached to a guide frame, which is attached to a wheeled base by pivotal telescopic couplings that permit each side arm of the frame to be adjusted axially and pivotally via a motorized rack and pinion system, independently of the other arm, in parallel vertical planes. An axially-displaceable transverse guide beam which is attached to the side arms carries a telescoping tool carriage. The apparatus can be used with paint stripping tool having a head with a ribbon seal, proximity sensors, and a gravity load equalizing adapter. During operation of the apparatus, the proximity sensors provide continuous feedback concerning the position of the head with respect to the fuselage.
Ashworth's apparatus, described in U.S. Pat. No. 4,294,188, includes a vehicle that carries an articulated, rotatable, hydraulically-actuated boom structure resembling those commonly found on fire trucks and power line maintenance equipment. A cage is pivotally connected to the outermost end of the upper boom; a frame, carrying rollers, is pivotally connected to the cage. In operation, the hydraulic system biases the turntable so as to maintain engagement between the rollers and the work surface. McGuire's hull-cleaning apparatus (U.S. Pat. No. 5,628,271) includes a steered, motorized vehicle that carries a high-pressure sprayer. The vehicle is supported on the surface of a ship hull by the adhesion force of a permanent magnet.
In U.S. Pat. No. 3,705,565, Hammelmann shows an apparatus that includes a telescoping mast mounted to a turntable and an evacuable container pivotably mounted to the upper end of the mast. The container, which has an open side with sealing rollers facing the work surface, contains two spray nozzles used for treating the surface (the sealing rollers constitute a support for accommodating the unevennesses of the surface). The container itself slides on a pair of guide rods which are mounted to the mast by ball bearing assemblies. The apparatus includes a hydraulic cylinder for tilting the mast. In U.S. Pat. No. 3,623,902, Hammelmann describes an apparatus that includes several hydraulic cylinders and a transverse jib that compensates for the reaction force acting upon the nozzle when water is ejected at high pressure, thereby helping ensure constant spacing of the work station from the surface being treated. A feeler actuates the drive which effects tilting of the mast, which is accomplished by another hydraulic cylinder.
Matsuno, et al. (GB No. 2,113,080) provide an apparatus having a pipe with a plurality of jet nozzles mounted to a wheeled support frame (a "parallelogrammic frame" with four side pieces rotatably connected to one another at the four corners). The pipe can be rotated and moved towards/away from the work surface by means of a series of hydraulic actuators. The Zauralov, et al. apparatus (SU No. 299,140) includes a tool-carrying head mounted to a parallelogram-manipulator platform. The platform, which is attached to a pair of pivotable arms, can be raised and lowered, or rocked about an axis, by hydraulic cylinders.
Vehicles that can move an instrument carriage both horizontally and vertically are satisfactory for many applications, including cleaning large, approximately planar areas of ship hulls, aircraft fuselages, storage tanks, and so forth. However, these types of apparatus are less useful for cleaning curved areas such as the bow, stern, and bottom of a ship, the bottom of an aircraft fuselage, or the walls of a storage tank, where effective cleaning depends on the ability to follow the surface contour. Furthermore, a ship is supported in dry dock by support blocks with (typically) only a five to six foot clearance underneath; aircraft may be even closer to the ground. Any useful vehicle must have a sufficiently low profile to access such confined spaces. Therefore, many dry docks and aircraft maintenance facilities still resort to costly, potentially-dangerous manual cleaning techniques for at least part of the surface maintenance process.
There is a need for a simple, reliable, low-profile, remotely-controllable, contour-following apparatus for cleaning ship hulls, aircraft fuselages, storage tanks, and like structures. Such an apparatus should be made with readily-available, modular components, be straightforward to operate, and have a profile that allows its user to access bottom surfaces and curved surfaces of hulls.